(1) Field of the Invention
The present invention relates to an optical switch and an optical switch module that are arranged to switch a propagation path of an optical signal.
(2) Description of the Related Art
An optical signal is preferable in transmitting a signal at fast speed and in large capacity. For a long-distance trunk communication system, transmission of an optical signal has been already realized for practical use. This kind of system is essentially required to have a function of switching a transmission path of an optical signal.
Traditionally, the switch of a transmission path of an optical signal has taken the steps of temporarily converting an optical signal into an electric signal, causing a semiconductor switch to switch to a signal destination, and then re-converting the electric signal into the optical signal. However, since transmission of a signal is made faster and faster, the transmission speed surpasses the speed of an electric switching system arranged through the use of a semiconductor switch.
Under these circumstances, a new optical switch has been developed which is arranged to switch a transmission path without converting an optical switch into an electric signal. For realizing this type of optical switch, several types of systems have been proposed. Of these systems, for example, a great concern is placed on an optical switch arranged to have an optical deflector element that provides a fast switching operation. The optical deflector element is composed so that crystals having an electrooptical effect, that is, the refractive index of which crystals is varied by an electric field, are used for composing a light waveguide (simply referred to as a waveguide) and a prism electrode is formed on the upper and the lower portions of the waveguide. The electrodes are excited to apply a voltage onto the waveguide so that an optical signal propagating through the waveguide may be deflected.
FIG. 11 is an illustration showing an exemplary arrangement of the conventional optical switch arranged to have an optical deflector element.
In FIG. 11, the optical switch 800 is arranged to have three input channels and four output channels. This optical switch 800 is arranged to have a waveguide input portion 810, a collimating portion 820, an input side optical deflector element portion 830, a common waveguide 840, an output side optical deflector element portion 850, a light-condensing portion 860, and a waveguide output portion 870. In this optical switch 800, for example, the waveguide input portion 810, the collimating portion 820, the common waveguide 840, the light-condensing portion 860, and the waveguide output portion 870 are integrally formed on the substrate, on which are mounted the input side optical deflector element portion 830 and the output side optical deflector element portion 850.
The waveguide input portion 810 includes input waveguides 811, 812 and 813 formed for three input channels, to which an optical signal enters. Likewise, the waveguide output portion 870 includes output waveguides 871, 872, 873 and 874 formed for four output channels, from which the optical signal outgoes.
The collimating portion 820 is composed of collimate lenses 821, 822 and 823 that correspond with the input waveguides 811 to 813 respectively. Each of the collimate lenses 821 to 823 is served to convert the rays outgoing radially from the input waveguides 821 to 823 into parallel rays and then inputs the parallel rays into the input side optical deflector element portion 830.
The input side optical deflector element portion 830 provides optical deflector elements 831, 832 and 833 for the input channels. In each of the optical deflector elements 831 to 833, two prism electrodes 831a and 831b served as a lower electrode and a conductive substrate (not shown) served as an upper electrode apply a voltage onto a slab waveguide (not shown) composed of a material having an electrooptical effect. The applied voltage causes the refractive index inside the slab waveguide to be varied and then the propagating direction of the incoming optical signal to be changed.
The common waveguide 840 is composed of a slab waveguide and serves to convey the rays passed through the optical deflector element portion 830 on the input side into the optical deflector element portion 850 on the output side.
The output side deflector element portion 850 includes optical deflector elements 851, 852, 853 and 854 that correspond with the output channels respectively. Each of the optical deflector elements 851 to 854 has the same structure as each of the optical deflector elements 831 to 833. The optical deflector element causes the propagating direction of the rays entered from the input side optical deflector element portion 830 through the common waveguide 840 to be changed, so that the resulting rays may be entered into the light-condensing lenses 861, 862, 863 and 864.
The light-condensing portion 860 includes four light-condensing lenses 861 to 864 that correspond with the output waveguides 871 to 874 included in the waveguide output portion 870 respectively. The light-condensing lenses 861 to 864 are served to condense the rays passing through the corresponding light deflector elements 851 to 854 included in the optical deflector element output portion 850 and then to guide the condensed rays into the corresponding output waveguides 871 to 874 of the waveguide output portion 870.
The optical switch 800 arranged as described above enables to switchably put the optical signal entered from each input channel into any one of the output channels by controlling the voltage applied onto each optical deflector element included in the optical deflector element input portion 830 and the optical deflector element output portion 850. Further, each optical deflector element can be used at a time in the optical deflector element input portion 830 and the optical deflector element output portion 850. Hence, the optical signals inputted into three input channels at a time are allowed to be conveyed into any one of the output channels.
However, the foregoing conventional optical switch is required to have the same number of optical deflector elements as the channel number at the input and the output sides of the optical signal. Likewise, it is also required to have the same number of independently-formed collimate lenses or light-condensing lenses as the input or the output channel number. As is understood from these requirements, the conventional optical switch has so complicated a structure that its manufacturing cost may not be suppressed so much.
Moreover, as the input and output channels are increasing in number, the request for reducing the optical switch in size is on the rise. If more channels are provided, for reducing the conveying length of an optical signal, it is necessary to enlarge an angle of deflection of the optical deflector element portion. For this purpose, it is necessary to raise a voltage to be applied in the optical deflector element portion or use a material with a refractive index greatly changed when the voltage is applied, which results in raising the power consumption or the manufacturing cost.
In a case that the optical switch arranged as described above provides an arrangement of one input to n output channels (1×n channels), the optical switch may be used for switching a plurality of optical signals on the input side into the signals on the output side at a batch. Herein, the terms of “switching . . . at a batch” means that n combinations of waveguides each having m output channels for m input channels are prepared so that the optical signals of m input channels may be outputted to any one of the waveguides at a batch.
For realizing this type of conversion at a batch, it is necessary to range only m optical switches each having one input and n output channels in parallel and, at a later stage, rearrange the output waveguides of each optical switch into n combinations of waveguides. Hence, this disadvantageously makes the overall length of the waveguides longer and the structure of the optical switch more complicated.